The Moon is Down; I have not heard the clock

post by chemslug · 2021-06-13T01:40:18.944Z · LW · GW · 5 comments

I wanted to share a quick post about something that's made me significantly happier over the past year: knowing what the phase of the moon is on any given day.  Importantly, I don't do this with any kind of computer tool.  It's a proxy for "am I spending enough time outside", but because I don't let myself cheat and rely on actually seeing the moon at least every few days, I've succeeded in not Goodharting myself, at least so far.

One of the things that helped me do this successfully was figuring out what time of day I could expect to see the moon during the different phases.  I know, I know, it's a trivial exercise in orbital mechanics, so maybe all of you do this instinctively, but it wasn't something anyone ever explained to me explicitly.  It actually took two disparate works of fiction to make the connection for me.

The first literary clue comes from my favorite Shakespeare play, Macbeth.  Scene II, Act I starts with Banquo and Fleance in the court of Macbeth's castle:

Banquo: How goes the night, boy?

Fleance: The moon is down; I have not heard the clock.

Banquo: And she goes down at twelve.

Fleance: I take't, 'tis later, sir

The second clue (here's where the penny really dropped) is from Cormac McCarthy's All the Pretty Horses, where the main character says "First quarter moon sets at midnight where I come from." 

Of course, the true first-quarter moon sets at midnight regardless of where you are because at (solar) midnight, the place you're standing is facing as far from the sun as it can be, and the first quarter moon means that the sun-moon-earth angle is a 90-degree angle.  (This is also true at the third-quarter moon, but at that phase, the moon comes up at midnight).

To be more explicit, at the new moon, the moon is almost between the sun and the earth (if it's exactly between, you get a solar eclipse!) so the moon rises and sets near when the sun does, but it's tough to see.  A waxing crescent moon comes up gradually later in the morning but is easiest to see shortly after sunset, just as it's going down.  The first-quarter moon comes up at noon and, as we've already covered, goes down at midnight.  Waxing gibbous moons come up in the afternoon and set in the early morning, before sunrise.  At the full moon, the earth is almost between the sun and the moon so the moon comes up around sunset and sets near sunrise.  The waning gibbous moon comes up gradually later after sunset and sets gradually later in the morning.  The third quarter moon rises at midnight and sets at noon.  Finally, the waning crescent moon comes up gradually later after midnight and sets in the afternoon. 

All of this is just to say: get outside, preferably with people you care about!  I look forward to being unwilling to shut up to the whippersnappers about how when I was young, the moon didn't have all those dots of light from the settlements.

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